Ensure Ephemeral driver always works with object clones

[orcinus]

Fix for #377

The Ephemeral driver methods Ephemeral::getData and Ephemeral::storeData use object references if data stored in cache is an object. This means that, e.g.

1. storing object $foo in cache
2. doing $foo->name = "not my name"
3. and then reading from cache will produce an object with name set to "not my name"

Obviously, the data stored in cache should not be a reference, and should be invariant except when changed through the cache driver itself.

Simple clone if data is an object, as implemented here, should do the trick. This could've been written as a nested ternary, but that would've been ugly/unreadable.

[coveralls]

Coverage decreased (-0.07%) to 94.987% when pulling 192488e on orcinus:orc-ephemeral-clone into a6f14f7 on tedious:master.

[orcinus]

Forgot to mention - the change in Ephemeral::storeData isn't really necessary, assuming nothing inside the driver will ever change the data. But, thought it might be a good idea (defensive programming) to clone the object there as well. Feel free to remove.

[Ruud-Zuiderlicht]

Forgot to mention - the change in Ephemeral::storeData isn't really necessary, assuming nothing inside the driver will ever change the data. But, thought it might be a good idea (defensive programming) to clone the object there as well. Feel free to remove.

I think cloning at storeData is required to prevent 3rd party code from storing, then changing the object from outside of the Ephemeral driver.

In any case, what is the status of this change?

[mbaynton]

I think that serialize() and deserialize() are better options than clone(), because that's what's used in the production drivers. The serialization/deserialization process is of course customizable, and if the Ephemeral driver does it the same way as the other drivers it allows me to write tests of my app that verify correct caching and serialization by just using the Ephemeral driver in the tests.

PHP's default clone also is a shallow copy so you're still going to have this issue with nested objects. This might also require developers to make their stuff clone properly in order to use it in tests when doing so isn't otherwise necessary.

[orcinus]

Good point.

[mbaynton]

As I'm coding this up, I actually like Ephemeral the way it is.

In production, I'm using the Composite driver to stack a limited-size Ephemeral layer on top of Redis. It's nice that those in-memory cache hits don't have serialization/deserialization overhead, and in the case of object graphs even more nice that the ephemerally cached objects retain objects they reference. Then I avoid making deep serialized copies of them (would be invalidation nightmare) in the more persistent cache by just customizing PHP's serialization behavior.

I'm trying out leaving Ephemeral as-is, but making a SerializingEphemeral extension as well for use in test.

[tedivm]

I've rebuild the test suite to work on Github- please rebase against the main branch and reopen this pull request if you're still interested in having it merged. Thank you!